How She-Male Birds Win the Girl

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Birds of prey have a macho image, but some male raptors look and
act feminine, fooling everyone into thinking they are females.

These she-males often win out in the end. They avoid conflicts
with other puzzled males, and yet they establish territories and
enjoy successful mating with females.

"Permanent female mimicry," as the phenomenon is called, has
already been confirmed in the shorebird ruff Philomachus
pugnax. Now a paper in the latest Royal Society Biology
Letters has determined that 40 percent of all sexually
mature marsh harrier Circus aeruginosus males exhibit
lifelong female behaviors and attributes.

Such female mimicry, also seen in fish, reptiles and insects,
appears to emerge most often in species with males that fight a
lot with each other.

"When intrasexual aggression is high, permanent female mimicry is
arguably adaptive and could be seen as a 'permanent
non-aggression pact' with other males," lead author Audrey
Sternalski and her colleagues explained.

Sternalski, a researcher at the Instituto de Investigación en
Recursos Cinegéticos in Spain, and colleagues François Mougeot
and Vincent Bretagnolle tested out their theory. They presented
plastic decoys representing each of the three types of birds --
males, she-males and females -- to each bird group during
different stages of their breeding cycles.

Typical males were aggressive toward male decoys, but more
tolerant of the she-males.

"By contrast," the researchers wrote, "female-like males
tolerated male decoys (both she-male and male) and directed their
aggression towards female decoys…Therefore, female-like males not
only look like females, but also tended to behave like them when
defending breeding resources."

Randolph Krohmer, an associate professor of biology at Saint
Xavier University, recently led a study on she-male red-sided
garter snakes, Thamnophis sirtalis parietalis. In this
species, the female mimics don't look like females, but they
release a pheromone that fools other snakes into thinking they
are gals instead of guys.

"During courtship these snakes form mating balls that can consist
of 50 males and one actual female," Krohmer told Discovery News.
"It looks like a tumbleweed rolling around on the ground."

He said the snakes "taste" the sex pheromone by flicking their
tongues. When males detect the chemical released by the
she-males, they sometimes spend time courting them. While these
males are busy being confused, the female mimics then make moves
toward the actual females.

"The she-males diminish the costs of courtship at the same time
as duping other males," said Morris Gosling, an emeritus
professor of evolutionary biology at the University of Newcastle.

Krohmer at first wondered if the behavior somehow benefited the
entire species, but he's been studying the snakes for decades.
When he began his work, approximately 10 percent of the snake's
population consisted of she-males. That has remained constant
over the years.

"You'd expect the percentage to go up if she-males were
advantageous to the species," he said.

Nevertheless, she-males persist and represent "a third category
of sexual behavior," which is neither fully male nor female,
according to Krohmer.